Research on children with Specific Language Impairment (SLI) has primarily focused on their expressive deficits. Relative to our understanding of these children's expressive difficulties, their receptive problems are poorly understood. This has led to underspecified theoretical accounts of SLI, a limited array of effective interventions to treat them, and less than favorable language intervention outcomes. The results of meta-analyses, systematic reviews, and clinical trials indicate that language intervention has a smaller effect on language comprehension than on language production (Cirrin & Gillam, 2008; Law et al., 2004; Bishop, et al., 2006). Recently, Leonard (2009) has argued that an inability to process linguistic information in the input is likely to play a prominent role in the comprehension difficulties of children with SLI. Debate exits as to whether the sentence comprehension problems in children with SLI reflect a deficit in the language system (the domain-specific view) or a general deficit in cognitive processing (the domain-general view). The primary goal of this large-scale project is to systematically determine which account provides the better descriptive and explanatory model to characterize sentence comprehension in children with SLI. The proposed 5-year project will address two related specific aims in five integrated studies. 450 children will participate: 150 children with SLI (ages 9;0-11;11), 150 age/nonverbal IQ matched (CA) children, and 150 younger children matched for short-term memory and vocabulary (YMV). Aim 1 employs a psychometric approach to investigate the relationship between several cognitive processing mechanisms (controlled attention, lexical retrieval, retrieval interference, short-term memory, working memory, and processing speed) and the comprehension of noncanonical sentences (Studies 1-2) or canonical sentences (Studies 3-4). We hypothesize that the modeling results will support the domain-general account. As part of this aim, we will also examine whether similar sets of cognitive mechanisms underlie sentence comprehension in children with SLI and CA children (with different a set likely subserving noncanonical and canonical sentences). Aim 2 more specifically examines working memory retrieval in noncanonical sentence processing to determine whether children with SLI fail or are slower to reactivate a prior constituent (NP1) during noncanonical sentence processing. We hypothesize they will be slower relative to CA children, supporting the domain-general view. Overall, the results may lead to four high impact implications for the field of SLI. First, a fundamentally new theoretical understanding of the relationship between cognitive processing and sentence comprehension may emerge. Second, models of normal adult and SLI sentence comprehension may be merged into a coherent developmental framework. Third, clinical cognitive-linguistic profiles of children with SLI will be expanded. And fourth, critical insights may emerge into which cognitive mechanisms could be targeted in alternative language treatments designed to improve the language comprehension of children with SLI.